The invention results to a method of measuring shifts in mountains and rock structures and an apparatus suitable therefor.
The measurement of shifts in mountains is very important since the results of basic tests according to German Industrial Standard 21521 show that shear stresses can yield the lowest deformation to failure of anchors in the structure. Up to now such measurements were only possible by optical observation (borehole endoscopy). These types of measurement were very expensive.
From German open application 17 73 862, a shear strip device is known for determining ground movements. In this case, shear formed into a tube were arranged in a borehole. Along the tubular shear strip extended two conductors, whereby between the conductors at regular intervals, resistances were arranged. The shear strips were mortared into the borehole and thus held in position. The mortaring of the shear strips into the borehole was very expensive and gave rise to significant difficulties when the borehole was vertical.
The invention has as its object to provide a simple and inexpensive method and apparatus for measuring shifts in rock structures.
With the method of the invention, initially a borehole is drilled in the rock structure and in this borehole an electrically conductive tube whose diameter corresponds to the borehole diameter is positioned. In the electrically conductive tube there is provided an insulated electrical conductor. Both the electrically conductive tube and the electric conductor are connected to an electric measuring device for continuity measurement.
The apparatus according to the invention is thus comprised of a metal tube, especially a steel tube, in which an insulated electrical conductor is arranged approximately parallel to its longitudinal extent. The steel tube is received in a borehole of approximately identical caliber. Both the steel tube and the electrical conductor are connected to an electrical measuring device for continuity measurement. In this built-in state, no continuity between the electrical conductor and the steel tube is detectable. Should there be a shift, however, in the rock strata or portions of the rock strata, in the anchor penetrating regions which move oppositely, the steel tube will initially be deformed. With further shifts, the steel tube will destroy the insulation of the electrical conductor and a continuity can be detected. When the continuity is detected, the measured travel amounts to:
Measured travel=(borehole diameter)xe2x88x92(2xc3x97tube wall thickness)xe2x88x92(conductor diameter)
The detection of the measured travel is basic to the test results in accordance with the principles of German Industrial Standard 21521. Within the framework of these principles, the load bearing and deformation properties of rock anchors under shear stress are investigated. For this purpose, anchors are built into a model rock structure (two concrete blocks: shear plane between both blocks) and then stressed. With the aid of such a characteristic curve, the properties of the built-in anchor under shear can be described. Starting from the maximum deformation at failure of the anchor, different measured travels for the deformation measurement in the rock structure can be determined.
With the aid of different borehole diameters and correspondingly matched apparatuses (metal tubes and insulated conductors) different travel measurements can be realized.
If, for example the steel tube wall thickness is 1 mm and the diameter of the conductor (without insulation) is 10 mm, the following measured travel is obtained for a bore diameter of 52 mm:
Measured travel 1=52 mmxe2x88x92(2xc3x971 mm)xe2x88x9210 mm=40 mm.
If the borehole diameter amounts to 32 mm, the result is:
Measured travel 2=32 mmxe2x88x92(2xc3x971 mm)xe2x88x9210 mm =20 mm.
It is also possible to provide a multiplicity of conductors of different lengths in the steel tube. In this manner, shifts for a multiplicity of different measurements at different horizontal levels can be determined.
It is also possible to arrange a multiplicity of steel tubes inside one another in a single borehole. In this manner multiple measured travel stages can be accommodated in a single borehole.
The aforementioned components which are used in accordance with the invention and are claimed and described in the example do not depend upon their size, shape, choice of material and technological concept for their effect so that they can be used practically without limitation to satisfy any criteria of choice in the respective field of use.